Photo-detector device and a method for biasing a photomultiplier tube having a current source for setting a sequence of voltage follower elements

Abstract

A photo-detector and method for operating same: the photo-detector comprises a photomultiplier tube comprising a plurality of electrodes, each having a photocathode, an anode, a first dynode, intermediate dynodes and a last dynode; and a biasing circuit that comprises a sequence of voltage follower elements, a voltage divider and a current source. The voltage divider is coupled across a high voltage power supply and different dynodes are coupled to different ones of the voltage follower elements, control inputs of which are coupled to different junctions of the voltage divider. The current source is coupled to the voltage divider, to the sequence of the voltage follower elements and to the cathode. The anode is coupled to a load element coupled to a positive pole of the high voltage power supply and arranged to receive an output signal of the anode and convert it to an output signal of the photo-detector.

We claim: 
     
       1. A photo-detector device comprising:
 a photomultiplier tube comprising a plurality of electrodes, the plurality of electrodes comprises a photocathode, an anode, a first dynode, intermediate dynodes and a last dynode; and 
 a biasing circuit that comprises a sequence of voltage follower elements, a voltage divider and a current source; 
 wherein the voltage divider is coupled across a high voltage power supply; 
 wherein different dynodes are coupled to different voltage follower elements of the sequence of voltage follower elements; 
 wherein control inputs of different voltage follower elements are coupled to different junctions of the voltage divider; 
 wherein the current source is coupled to the voltage divider, to the sequence of the voltage follower elements, to the cathode and to a negative pole of the high voltage power supply such that the current source sets the current in the sequence of voltage follower elements; and 
 wherein the anode is coupled to a load element coupled to a positive pole of the high voltage power supply and arranged to receive an output signal of the anode and convert it to an output signal of the photo-detector device. 
 
     
     
       2. The photo-detector device according to  claim 1 , wherein the current source is coupled between the first dynode and the cathode. 
     
     
       3. The photo-detector device according to  claim 1 , wherein a voltage follower element of the sequence of voltage follower elements is coupled between the cathode and the first dynode, and the current source is coupled between the negative pole of a high voltage power supply and the cathode. 
     
     
       4. The photo-detector device according to  claim 1 , wherein the voltage follower element comprises a transistor. 
     
     
       5. The photo-detector device according to  claim 1 , wherein the voltage follower element comprises a transistor and a Zener diode. 
     
     
       6. The photo-detector device according to  claim 1 , wherein the biasing circuit further comprises a first sequence of capacitors that are each coupled in parallel to a resistor of a sequence of resistors of the voltage divider. 
     
     
       7. The photo-detector device according to  claim 6 , comprising a second sequence of capacitors, wherein each capacitor of the second sequence of capacitors is coupled between a pair of dynodes. 
     
     
       8. The photo-detector device according to  claim 1 , wherein the biasing circuit further comprises a first capacitor coupled in parallel to the voltage divider. 
     
     
       9. The photo-detector device according to  claim 1 , comprising a sequence of capacitors, wherein each capacitor of the sequence of capacitors is coupled between a pair of dynodes. 
     
     
       10. The photo-detector device according to  claim 1 , wherein the current source is arranged to supply a constant current to the voltage divider and wherein the voltage follower elements are arranged to output a substantially constant voltage regardless of changes in current drained by the dynodes. 
     
     
       11. The photo-detector device according to  claim 1 , arranged to operate with a gain that does not exceed 10,000. 
     
     
       12. A method of operating a photo-detector device, the method comprises:
 converting light impinging on a cathode of a photomultiplier tube of photo-detector device to an output signal of the photo-detector device; and 
 maintaining, by a biasing circuit of the photo-detector device, a voltage of each dynode of a plurality of dynodes of the photomultiplier tube, substantially constant regardless of changes in current drained by the dynode; 
 wherein the plurality of dynodes comprise a first dynode, intermediate dynodes and a last dynode; 
 wherein the photomultiplier tube further comprises an anode and a cathode; 
 wherein the biasing circuit comprises a sequence of voltage follower elements, a voltage divider and a current source; 
 wherein the voltage divider is coupled across a high voltage power supply; 
 wherein different dynodes are coupled to different voltage follower elements of the sequence of voltage follower elements; 
 wherein control inputs of different voltage follower elements are coupled to different junctions of the voltage divider; 
 wherein the current source is coupled to the voltage divider, to the sequence of the voltage follower elements, negative pole of the high voltage supply and to the cathode such that the current source sets the current in the sequence of voltage follower elements; and 
 wherein the anode is coupled to a load element coupled to the positive pole of the high voltage supply and arranged to receive an output signal of the anode and convert it to an output signal of the photo-detector device. 
 
     
     
       13. The method according to  claim 12 , wherein the current source is coupled between the first dynode and the cathode. 
     
     
       14. The method according to  claim 12 , wherein a voltage follower element of the sequence of voltage follower elements is coupled between the cathode and the first dynode, and the current source is coupled between a negative pole of a high voltage power supply and the cathode. 
     
     
       15. The method according to  claim 12 , comprising operating the photo-detector device with a gain that does not exceed 10,000.